The Texas Tornado (4spd crawler)

[AndyCW]

After my last truck with a two speed transmission and air lockers, I decided to try more gears in my transmission. I searched for transmission ideas and came across the regular four speed transmission. The common wisdom is that driving rings cannot handle any torque. This is accurate. I had to increase the gear reducton in the axles and step up the motor on the transmission input to reduce the torque that the transmission "felt". I also maded the linkage from the servo to the driving ring incapable of being backdriven. It still pops occasionally, but reengaging the driving rings with the servos clears it up.

It also has a neutral gear and this allows it to roll after the throttle has been released. Eliminating any extra gear exchanges to improve efficiency, reducing weight, and maintaining a rigid structure for the transmission to operate within became critical. I tried to get rid of the knob gears connected to the rc buggy motors outputs, but was unsuccessful.

• 12t to 12t ground the gears down
  
• 20t to 20t also ground the gears down
  
• 24t to 24t crown would not fit.
  

Caster angle on front axle is accomplished by less angle on the lower links. I tried a wider version of the LPE power unimog axle that has kingpin inclination. It worked and did not fall apart, but its turning radius was larger than a traditional steering axle and so it was discarded. It still is assembled, just not mounted on the truck. I made air lockers based off of the new 3 stud wide differential, but ended up discarding them because they added unnecessary complication. I killed several u joints on the driveshaft before I moved up to 9:1 reduction in the axle. The u joints that are installed have wax string wrapped around the ends and a small piece of heat shrink tube over that. This is a repair because all of my joints are now cracked.

If a tire becomes blocked in first gear with the steering turned, this design can quickly destroy u joints in the axle. There are a couple of altered pieces. 3l bars have had a couple of mm ground off to secure the towballs on the chassis and there is a 4.5 stud axle going to the knob gear on the transmission input. Both elements could be done without. It would require some redesign though. Moving to a 9398 style suspension and increasing the wheelbase would eliminate both of these issues.

I used 4l bars to secure the towballs in the axles. They fit into the back of the towball and prevent it from popping out of the lift arm.

Questions, comments, concerns, relevant war stories????

v/r

Andy

[DLuders]

What a great combination of light weight, climbing/crawling ability, and articulation! The 4-speed transmission is especially good. How long do those Power Functions rechargeable batteries last with those "thirsty" RC Buggy motors?

[z3_2drive]

like I said on youtube, amazing truck, and the need for parts like this:

is now very urgent... I like the shifting mechanism especially, I may do a bit of re-designing and try using a servo, but for now I need to make a BL order EDIT: you never showed it in 4th gear...too fast?

Edited April 21, 2013 by z3_2drive

[Boxerlego]

Nice job! That is a excellent video you have made. I've got two broken U-joints and been thinking about how to fix them and make it stronger. The heat shrink tubing is a neat idea around the broken u-joint. Are you going to use the tubing to strengthen the future u-joints?

[rm8]

Clever design using servo motors.

Where is demo of 4th gear?

You are the real king of hammers;)

[AndyCW]

Fourth gear is a little too weak for off road terrain. On flat level smooth surfaces it is fine, but it is hard to keep up with it using IR remote control. I am thinking about making a custom 9.6 Vdc battery pack. This would enable 4th gear to be used for much more, but make keeping up with it even harder. The lack of differentials cause it to bind and slow down significantly in fourth gear when turning. Using unimog tires may solve all of these problems. They have less grip, less diameter, and less mass. This makes them easier to turn. This might also solve what little gear popping remains in the driving rings.

Another way to reinforce/fix u-joints is to wrap the end in string and then soak the string in superglue.

Batteries were fully charged just before the video began. It should last longer than anyone will want to play with it. I have not had it run out of juice during testing. The math should be fairly easy to do. Max current allowed by IR rx and batteries combined with the capacity of the batteries. Ohms law and all that.

v/r

Andy

[timslegos]

Looks like it drives very well, I am impressed with the speed and ability. i would love to see more detailed pictures of the truck.

tim

[Alasdair Ryan]

Nice crawler Andy pandy.

Your crawler has good speed and good off-roading ability.

i would love to see more detailed pictures of the truck.

tim

So you can copy it and clam it as yours?

[Someonenamedjon]

So you can copy it and clam it as yours?

maybe he will add an extra pin and call it his to avoid copyright issues

[AndyCW]

I don't have many pictures other than what is in the slideshow portion of the video. Are there any specifics people would like to see?

The axles are pretty simple

8t to 24t portal hubs

12t to 36t spool

four links

12t gear on rack for steering

Transmission is this using the input shaft with the 24t gear on it instead of the 8t. The shifter linkage from servo to driving ring should be fairly straightforward from the video.

Allanp provided this picture on a previous thread of the gear exchange used.

v/r

Andrew

[Doc_Brown]

WOW, amazing Crawler. I love that 4 speed, can't believe that you fitted it in such small space. Can't wait for your next one. :thumbup:

Had a feeling those servos would be great for gear boxes.

Edited April 22, 2013 by Doc_Brown

[costabkz]

What a great combination of light weight, climbing/crawling ability, and articulation!

[Kevinatorrr]

What a great combination of light weight, climbing/crawling ability, and articulation!

deja vu!

[AndyCW]

LDD file of the chassis. This is my first LDD experience and as such this file is rough, but it should help people build their own four speed crawlers. It is incomplete and not identical to the real deal, but the key structures are there. The axles are nothing special. The upper and lower towball mounts have an altered 3l bar between them. This helps locate the front gear brace and stops the towballs from backing out.

Because of the models I used for the 5292 motor and the servo the instructions are a laugh.

http://www.filedropper.com/4spdcrawler

This is my first exposure to filedropper.

v/r

Andy

[allanp]

Nice gearbox

Your crawler works great, it's faster and more powerful than 9398

[hrontos]

It looks like a lot of fun to drive it. Very nice 4speed design. Good job.

[AndyCW]

Nice gearbox

Thanks for the inspiration.

v/r

Andy

[Lakop]

A great model and to add gears in such a compact way is very clever. The only negative, and it's not a criticism of the builder, is the amount of motors and battery boxes required.

H

[Zerobricks]

Just one thing. I see you used knob gears. Why not use bewel gears? They run much smoother and are more efficient.

[AndyCW]

I tried using 12t bevel gears and 20t bevels, but no mater how I braced them I could not get them to stop popping. The direct output of two 5292 motors overwhelmed them everytime. I even used this

and the 12t bevels kept popping.

I would change something in the bracing, reassemble, test, fail, teardown, and repeat till I was blue in the face. It turned out that the only thing I could come up with that would not pop was the knob gears. I even tried the 24t and a 24t crown. The larger tooth count would provide more contact for the teeth and maybe help, but is difficult to brace this setup in a studless design and it didn't fit.

They were all I could manage. I am open to suggestions on how to eliminate them.

v/r

Andy

[AndyCW]

A great model and to add gears in such a compact way is very clever. The only negative, and it's not a criticism of the builder, is the amount of motors and battery boxes required.

H

I understand where you are coming from and do not take any offense to criticism. It is necessary in a creative arena to be able to take the good and the bad without getting "butt hurt".

The power requirements for high speed necessitate multiple motors and batteries. The desire to be able to crawl and cruise necessitates a gearbox. Fewer elements means in this case less capabilities. I did remove the PF medium motor that powered the autovalve for the air locking differentials and the differentials themselves. As well as plans to make the rear axle steer. All in pursuit of simplicity and weight reduction.

v/r

Andy

[piterx]

I dont really like the overall look BUT performances are F Amazing man!!!! Great job